Jealousy

Sarah • 22

How do you ladies get over jealousy? My boyfriend and I have a mutual friend who is a girl. I trust him 100% but I don't trust her. She talks to him and sees him more than she does with me. She's a very flirty person which is why I don't like them talking. They will go shopping together too, and my boyfriend hates to shop. I hate feeling this way and I'm sick of it causing so many fights between us, what can I do???